Dimpling apparatus



Patented i ov. 2, 1943 O wE DIMPLING APPARATUS Howard R. Fischer, Detroit, Mich, assignor to Chicago Pneumatic Tool Company, New York, N. Y a corporation of New Jersey, V

Application October 13, 1942, Serial No. 461,855

4 Claims. (01. 153-21) This invention relates to apparatus for forming dimples around rivet holes in thin metal sheets to adapt them for the reception of flush type rivets; It has particular reference to a draw pin which extends through the hole and forms part of the'means for applying force between two opposed dies.

Flush rivets are used extensively in aircraft construction on the exposed surfaces of the metal skin which forms a cover for the fuselage; wing sections and other structural elements; The metal sheets, usually made of aluminum alloy, are mounted in place and the overlapping portions thereof are provided with registering perfora tions formed by drilling or punching. The sheets are dimpled around the holes to provide recesses for receiving the heads of the rivets. The resulting structure has the advantages of increased strength of the rivet joint resistance.

According to'one method'of dimpling, which is considered to be the most effective for certain types of work, a draw pin is inserted from one side of the sheets through the rivet hole and the projecting end on the other side is grasped with a power tool which applies pressure .to opposed dimpling dies through the application of tensile force to the draw pin. As soon as the dimple is formed, the draw pin is retracted and moved to the next hole. The cycle of operation must-necessarily be repeated in rapid succession because of the thousands of holes required to be dimpled in a single airplane. In the development of this method, it was found that the draw pins fre-' quently broke under the repeated strains and that the release of .the forces on the pin at the instant of breakage. caused the free end to be projected like a bullet. This not only endangered the operator but also resulted in loss of time, and excessive cost of replacement of dimpling apparatus.

Among the objects of the invention are the prevention of accidents, the provision of means for moving the pin from one rivet hole to another with greater facility, and to minimize waste of time and materials in reconstructing parts of the dimpling apparatus following breakage of the pin.

A feature of the inventionresides in anextension on the draw pin which is adapted to be connected to a holder. Another-feature resides in a clip which prevents the die from becoming accidentally separated from the broken end of the pin, but which permits the die to be readily transferred to a new pin.

and decreased Wind will appear more clearly" from the description which follows.

' In the accompanying drawings: j

Fig. l'is aside elevation partly in section showing a draw pin arranged inoperative relation to a holder and to a power tool; f'

Fig. 21s an elevational view showing therelation between the holder and the pm when the I latter breaks;

Fig, 3 is a side elevation partly in section of a draw pin positioned to be attached-to a power showing the shape tool and supported by a'holder of modified form;

Fig. 4 is' a longitudinal section through'a part 'of'thepower' tool shown in'Fig. 1; ona larger scale;

Fig. 5 is an elevational view of the'draw pin on a much larger scale, showing in section the pin, one of the dies, and fragmentary parts" of the holder and sheet metal;

Fig. 6- is a crosssection; as indicated hythe arrows 6 in Fig. 5;.

Fig. 7 is a longitudinal section of the clip itassumes when detached from the die;

Fig. 8'is a' view partly in elevation and partly in longitudinal sectionof" a modified pin and holder assembly; and 1 Fig. 9 is a fragmentary view of "another modifled pin and holder assembly.

.The dimpling apparatus of the present invention is designed to operate on the overlapping portions of two thin metal sheets H and I2 after they have been provided with registering perforations l3 formed by drilling or punching. The

has a head 2| against which the recessed die I4 is seated. 1

A power tool-may be provided for pulling pin 28 and the recessed die while applying the reactive force .against :the die ,,|5.- One embodiment of a tool for this purpose is. described herein and not. claimed, per se. Itjcomprises a cylinder 22, a piston 23 recipro'cab-le therein, a chuck 24 at the front end of the piston'l'or grasping the rear end of the draw pin Zil, a pair,of casing sections 25 and 26 connecting the cylirider,22

with the die I5, and a rubber abutment'member Other objects and features of the invention 5 7 adap d t press forwardly against the metal sheets during the dimpling operation. The piston is rcciprocated by pressure fluid, preferably oil, supplied through front and rear cylinder passages 28 and 29 respectively, which extend through a handle 3!! and which are controlled by Chuck 24 comprises an internally tapered sleeve 34, a plurality of radially moveable jaws 35, and a spring-pressed plunger 36 urging the jaws forward into camming engagement with the sleeve. The inner surfaces of the iawshave arcuate grooves arranged to grip the circumferentially grooved portion 31 near the rear end of the draw pin 20. The sleeve 34 has a screwthreaded connection with piston 23.

In use, the draw pin is inserted through a preformed opening l3 in sheets II and i2 until the recessed die |4 abuts against sheet The power tool is held in position to receive the grip portion 31 of the draw pin 20., The trigger 3| is pressed, thereby operating remote control mechanism (not shown) to initiate flow of hydraulic pressure fluid through passage 28 to pull piston 23 rearwardly. The chuck 24 pulls the draw pin- 23 which in turn draws the recessed die l4 into tight engagement with sheet II. The reaction of the pulling force moves the cylinder 22, casing sections 25 and 26, and the frusto-conical die l5 forwardly, thereby dimpling or flanging the metal sheets into the shape shown in Fig. 5. A part of the reaction is also transmitted to the rubber block 21 which supports the sheet metal at the circumference of the dimpled portion.

The draw pin or mandrel is made of hardened steel and has a tensile strength which is generally not much greater than the maximum applied stress, due to the annular recesses in the portion 31 and to the fact that the outer diameter is limited by the size of the drilled hole,.

for example one-eighth inch. The strain of repeated operations eventually results in fatigue failure of the steel whereupon the pin breaks.

Just before the pin snaps, very heavy strains are present in various parts of the machine. Likewise severe strains are setup in the pin which are manifested by a considerable stretch or elongation before the elastic limit is reached and a fracture of the pin occurs. All these strains represent potential energy which is instantly released upon breakage of the pin and threaded from the head 2| to the front extremity of the pin 20. The threaded extension forms -a detachable connection with a tapped opening in the flanged end of a holder 39. The main part of the holder extends perpendicular to the sheet metal .and terminates, in a knurled portion 4|! providing a handle grip for the operator.

.The recessed die i4 is detachable from the draw pin 20 and may be transferred from one pin toanother as the pins break. According .to one feature of this invention, the die loosely surrounds shank l8 and seats against a shoulder 4| on the pin head 2|, said shoulderand the complementary surface on the die having a nonlocking taper. This permits the die to be removed fromtthe pin by hand. Prior to this invention, it was the practice to make a press fit between the die and the pin. Whenever a pin broke, it was necessary to take the parts to an arbor press to remove the broken pin from the die. To obviate the need for a press fit with its resulting inconveniences, a quick detachable connection is herein provided. It comprises a clip 42' having a disc portion 43 provided with a central perforation 44 whereby the disc may surround the draw pin and may be clamped between the pin head 2| and the holder 33. Ex-- tending rearwardly from the disc portion is a pair of integral spring laws 43 adapted to receive the die l4 therebetween. As shown in Fig. 7, the clip when unattached is of such shape that the iawstaper rearwardly toward each other. To attach them to the die l4 they must be sprung into parallel relation thereby providing sufllcient tension to hold the die against, n iovement away from the tapered shoulder 4|.

This provides a friction lock for the die which prevents accidental separation but permits removal of the die relative to the pin at the will of the operator.

Summarizing the operation; two operators are located respectively on opposite sides of the metal sheets II and I2, one grasping the holder 39 and the other the grip handle 33 of the power tool. The holder 33 forms a unitary structure with the draw pin 23, recess die l4, and clip 42, and by manipulating the holder the pin may be inserted through the drilled holes II at the start of the dimpling operation. The power tool is advanced until the chuck jaws 35 pass over the grip portion 31 of the draw pin, and the trigger 3| is then pressed. This starts the power stroke of the tool, pulling the draw pin 20 and recessed die, 14 rearward, while applying an equal and opposite pressure to the frusto-conical die I! and rubber block 21. The opposing pressures on dies l4 and I! dimple or squeeze the metal sheets I, I2 into the shape shown in Fig. 5. The trigger 3| is then released to cause the hydraulic pressure fluid to reverse the piston stroke whereupon the chuck 24 releases its grip on pin 23. The operators then move their respective appliances to the succeeding drilled hole. The operations are repeated in rapid succession and it is only a matter of time before the draw pin breaks. The point at which breakage most frequently occurs is at the foremost groove on grip portion 31 as shown in Fig. 2. Immediately following the rupture, the front end of the pin tends to be projected under the influenceof stored energy, as in the case of prior devices. g The escape of the pin is prevented however by-the attached holder 39, which is much heavierthan the pin and which absorbs the shock tending to propel the latter. The broken pin is unscrewed from the, holder and removed from the die l4 and clip 42 by hand. Another pin is then substituted thereby permitting the die, clip, and holder to be used repeatedly.

From the above description it is apparent that the holder 39 not only protects the operator against possible injury but also functions to facilitate insertion of the draw pin into the metal sheets. Moreover, the holder cooperates with the clip 42 to prevent the die H from becomin lost when the pin 20 breaks.

Fig. 3 shows a modified form of holder 41 d ""v oeziding a dot strip of metal. The

. to metal sheets instead of perpem ,1 1

ermit it to be grasped directly by the hand. Ede knob has the advantage of fitting into close quarters but the diseclvsotsge that its mass ot very large in relation to the weight of In order to reduce the size of the broken ion, the pin is provided with a neck 56 werdly of the head 5i. The neclz is recessed to such an extent that the tensile strength is sli' htly weaker at the neck then at the pull grooves When e rupture occurs, the larger part of the pin remains in the grip of the power tool while only a small portion at the front end tends to be projecwd and can easily be held by the operator.

9 shows e. further modification in which the draw pin has a neck 55, head 5? and extension 58 adapted to perform the some functions as the corresponding elemenm in 8. The extension instead of being screw-threaded is generally cylindrical and is secured to a rubber knob 59 by vulcanization. if desired o series of annular grooves oil may be provided to strengthon the grip of the rubber knob.

What is claimed is:

1. Dimpliog apparatus comprising 2, drew pin having a shank excendirig through as hole in is metal sheet and being inserted from the front side to the rear side of the metolje grip portion on the pin near its rear end, a shoulder on the pin near its front end, a recessed die seated against sold shoulder and engegeaole with the front fees of the sheet around the hole, a compiementary frusto-conioal die engageeble with the rear face of the sheet around the'holeopower means for pulling the pin at said grip portion and for transmitting the reaction of the pulling force to the frusto-conicel die, a. screw-threaded por tion at the front extremity of the pin, and is threaded handle secured to said screw-threaded portion, said handle providing manual means for holder has a grip portion 38 extending sale ' on the pin near the front end, as removable die mounted on the shank and see-ted egsinst said shoulder arid having a recessed port engageable with the front face oi the sheets around the opening, a complementary irusto conical die engagesole with the rear face of the sheets around opening, power means for pulling the pin st said grip oer-tics. end for transmitting the reaction oi the pullizig force to the frustoconical die, an integral extension at the front or tremity of the pin :9, handle secured to said extension, said handle providing manual means for inserting the draw pin through the holes and also for restraining the pin in the event of breakage and releasable means for securing the recessed die against rearward movement away from the shoulder.

3. Dillipling apparatus for sheet metal comprising e poir of complementary dies engageable with opposite sides of the metal, a draw pin adopted to extend through said dies and through on opening in sold motel, power means for pulling said pin and applying the reactive force to one of sold dies, as heed on said pin for applying the pulling force to the other of said dies, on extension on said pin beyond said-heed, and s holder having a, grip portion extending parallel to the sin and having as flanged portion provided with o topped openinmseid pin extension being screw-threaded to form at detachable connection with seid topped opening.

Dimplirie: apparatus comprising e drew pie. he /log s, a shoulder at forward end oi 'Zhe shook, die having a shoulder eomple meeting the shoulder on the shoulders having e, noiideclring teoer to permit separation:

- of the dieiroiri the pin, sold having a head 

